Sheath



FIG. 1 is a front elevational view of a sheath showing my new design;

FIG. 2 is a right side elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a top plan view thereof; and

FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 1. 

The ornamental design for a sheath, as shown and described. 